Shoes are the main cause of most of the running injuries. If his shoes are worn , get new ones. Two or three pairs of shoes can help prevent shin soreness.Regular exercise also helps to prevent sore shins, by helping to maintain a body alignment such that the foot tends to land under, rather than in front of, the runner. It follows that overstriding is a major cause of splints.
Is he only running on hard surfaces? Is he running hard everyday. I found being in the wrong shoes , and I think running hard everyday on the roads is a formula for success.
That is if success if always having shin splints. Depending on the area it could be a weakened muscle or possibly compartment syndrome